Define a class named document that contains an instance variable of type string named text that stores any textual content for the document. create a method named tostring that returns the text field and also include a method to set this value. next, define a class named email that is derived from document and includes instance variables for the sender , recipient , and title of an email message. implement appropriate accessor (get) and mutator (set) methods. for example get and set method for sender variable. the body of the email message should be stored in the inherited variable text . redefine the tostring method to concatenate all text fields. similarly, define a class named file that is derived from document and includes a instance variable for the pathname . the textual contents of the file should be stored in the inherited variable text . redefine the tostring method to concatenate all text fields. finally, create several sample objects of type email and file in your main method. test your objects by passing them to the following subroutine that returns true if the object contains the specified keyword in the text property. public static boolean containskeyword(document docobject, string keyword) { if (docobject.(keyword,0) > = 0) return true ; return false ; }